In multispectral imaging, photometric invariants pose great opportunities and challenges in the areas of material identification [14] and shape analysis. This is due to the information-rich representation of the surface radiance acquired by multispectral and hyperspectral sensing devices, which deliver wavelength-indexed spectral data, i.e. reflectance or radiance data, in thousands of bands across a broad spectrum. As in trichromatic imaging, multispectral reflectance distribution is determined not only by the light source and viewer directions, but also by the material properties of the surface under study.
In computer vision, the modeling of surface reflectance is a topic of pivotal importance for purposes of surface analysis and image understanding. For instance, Nayar and Bolle [42] have used photometric invariants to recognise objects with different reflectance properties.
Since the recovery of illumination spectrum and material reflectance are mutually interdependent, colour constancy is also an issue. Colour constancy is the ability to resolve the intrinsic material reflectance from their trichromatic colour images captured under varying illumination conditions. The research on colour constancy branches in two main trends, one of them relies on the statistics of illuminant and material reflectance, the other is drawn upon the physics-based analysis of local shading and specularity of the surface material.
This disclosure concerns physics-based colour constancy that analyses the physical processes by which light interacts with material for the purpose of illuminant and surface reflectance estimation. The two methods of physics-based colour constancy are Land's retinex theory [35, 36] and the dichromatic reflection model [48]. Land's retinex theory has inspired several computational models of human colour constancy [7]. On the other hand, the dichromatic model describes reflected light as a combination of the body reflection and surface reflection (highlight), which treat the illumination estimation problem as an analysis of highlights from shiny surfaces [32, 33, 39, 53].
U.S. Pat. No. 7,443,539 (Olympus) determines spectral data characteristics of an image and requires a spectrometer (42) and reference plate (51) to compensate for the illuminant.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.